Specific Absorption Rate Measurement and Energy-Delivery Device Characterization Using Image Analysis

ABSTRACT

A method of controlling output of an electrosurgical power generating source includes the steps of receiving image data including tissue temperature information of a target tissue volume, calculating a specific absorption rate as a function of the tissue temperature information from the image data, and determining one or more operating parameters associated with the electrosurgical power generating source based on the calculated specific absorption rate.

BACKGROUND

1. Technical Field

The present disclosure relates to a system and method for measuring thespecific absorption rate of electromagnetic energy emitted byenergy-delivery devices, such as energy-emitting probes or electrodes,and, more particularly, to specific absorption rate measurement andcharacterization of energy-delivery devices using image analysis.

2. Discussion of Related Art

Treatment of certain diseases requires the destruction of malignanttissue growths, e.g., tumors. Electromagnetic radiation can be used toheat and destroy tumor cells. Treatment may involve inserting ablationprobes into tissues where cancerous tumors have been identified. Oncethe probes are positioned, electromagnetic energy is passed through theprobes into surrounding tissue.

In the treatment of diseases such as cancer, certain types of tumorcells have been found to denature at elevated temperatures that areslightly lower than temperatures normally injurious to healthy cells.Known treatment methods, such as hyperthermia therapy, heat diseasedcells to temperatures above 41° C. while maintaining adjacent healthycells below the temperature at which irreversible cell destructionoccurs. These methods involve applying electromagnetic radiation toheat, ablate and/or coagulate tissue. Microwave energy is sometimesutilized to perform these methods. Other procedures utilizingelectromagnetic radiation to heat tissue also include coagulation,cutting and/or ablation of tissue. Many procedures and types of devicesutilizing electromagnetic radiation to heat tissue have been developed.

In treatment methods utilizing electromagnetic radiation, such ashyperthermia therapy, the transference or dispersion of heat generallymay occur by mechanisms of radiation, conduction, and convection.Biological effects that result from heating of tissue by electromagneticenergy are often referred to as “thermal” effects. “Thermal radiation”and “radiative heat transfer” are two terms used to describe thetransfer of energy in the form of electromagnetic waves (e.g., aspredicted by electromagnetic wave theory) or photons (e.g., as predictedby quantum mechanics). In the context of heat transfer, the term“conduction” generally refers to the transfer of energy from moreenergetic to less energetic particles of substances due to interactionsbetween the particles. The term “convection” generally refers to theenergy transfer between a solid surface and an adjacent moving fluid.Convection heat transfer may be a combination of diffusion or molecularmotion within the fluid and the bulk or macroscopic motion of the fluid.

The extent of tissue heating may depend on several factors including therate at which energy is absorbed by, or dissipated in, the tissue undertreatment. The electromagnetic-energy absorption rate in biologicaltissue may be quantified by the specific absorption rate (SAR), ameasure of the energy per unit mass absorbed by tissue and is usuallyexpressed in units of watts per kilogram (W/kg). For SAR evaluation, asimulated biological tissue or “phantom” having physical properties,e.g., dielectric constant, similar to that of the human body isgenerally used.

One method to determine the SAR is to measure the rate of temperaturerise in tissue as a function of the specific heat capacity (oftenshortened to “specific heat”) of the tissue. This method requiresknowledge of the specific heat of the tissue. A second method is todetermine the SAR by measuring the electric field strength in tissue.This method requires knowledge of the conductivity and density values ofthe tissue.

The relationship between radiation and SAR may be expressed as

$\begin{matrix}{{{SAR} = {\frac{1}{2}\frac{\sigma}{\rho}{E}^{2}}},} & (1)\end{matrix}$

where σ is the tissue electrical conductivity in units of Siemens permeter (S/m), ρ is the tissue density in units of kilograms per cubicmeter (kg/m³), and |E| is the magnitude of the local electric field inunits of volts per meter (V/m).

The relationship between the initial temperature rise ΔT (° C.) intissue and the specific absorption rate may be expressed as

$\begin{matrix}{{{\Delta \; T} = {\frac{1}{c}{SAR}\; \Delta \; t}},} & (2)\end{matrix}$

where c is the specific heat of the tissue (or phantom material) inunits of Joules/kg-° C., and Δt is the time period of exposure inseconds. Substituting equation (1) into equation (2) yields a relationbetween the induced temperature rise in tissue and the applied electricfield as

$\begin{matrix}{{\Delta \; T} = {\frac{1}{2}\frac{\sigma}{\rho \; c}{E}^{2}\Delta \; {t.}}} & (3)\end{matrix}$

As can be seen from the above equations, modifying the localelectric-field amplitude directly affects the local energy absorptionand induced temperature rise in tissue. In treatment methods such ashyperthermia therapy, it would be desirable to deposit an electric fieldof sufficient magnitude to heat malignant tissue to temperatures above41° C. while limiting the SAR magnitude in nearby healthy tissue to beless than that within the tumor to keep the healthy cells below thetemperature causing cell death.

SAR measurement and the characterization of energy-delivery devices mayensure clinical safety and performance of the energy-delivery devices.SAR measurement and characterization of energy-delivery devices maygenerate data to facilitate planning and effective execution oftherapeutic hyperthermic treatments.

SUMMARY

The present disclosure relates to a method of controlling output of anelectrosurgical power generating source including the steps of receivingimage data including tissue temperature information of a target tissuevolume, calculating a specific absorption rate as a function of thetissue temperature information from the image data, and determining oneor more operating parameters associated with an electrosurgical powergenerating source based on the calculated specific absorption rate.

The present disclosure also relates to a method of controlling output ofan electrosurgical power generating source including the initial step ofproviding an energy applicator including a radiating section. The energyapplicator is operatively associated with an electrosurgical powergenerating source. The method includes the steps of positioning theradiating section of the energy applicator at a first position fordelivery of energy to a target tissue volume and transmitting energyfrom the electrosurgical power generating source through the radiatingsection to the target tissue volume. The method also includes the stepsof acquiring a first set of image data including tissue temperatureinformation of the target tissue volume by imaging the target tissuevolume using one or more imaging modalities, calculating a specificabsorption rate as a function of the tissue temperature informationobtained from the first set of image data, and controlling output of theelectrosurgical generator based on the calculated specific absorptionrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Objects and features of the presently disclosed system and method forspecific absorption rate measurement and characterization ofenergy-delivery devices and the presently disclosed electrosurgicalsystem and methods for controlling output of an electrosurgical powergenerating source will become apparent to those of ordinary skill in theart when descriptions of various embodiments thereof are read withreference to the accompanying drawings, of which:

FIG. 1 is a schematic illustration of a thermal profiling systemincluding an energy applicator array positioned for the delivery ofenergy to a targeted tissue area according to an embodiment of thepresent disclosure;

FIG. 2 is a perspective view, partially broken-away, of an embodiment ofa test fixture assembly in accordance with the present disclosure;

FIG. 3 is an exploded, perspective view, partially broken-away, of thetest fixture assembly of FIG. 2 shown with a thermally-sensitive mediumaccording to an embodiment of the present disclosure;

FIG. 4 is a perspective view, partially broken-away, of test fixtureassembly of FIGS. 2 and 3 according to an embodiment of the presentdisclosure shown with an energy applicator associated therewith;

FIG. 5 is a cross-sectional view of an embodiment of athermally-sensitive medium including a cut-out portion in accordancewith the present disclosure;

FIG. 6 is a perspective view of a support member of the test fixtureassembly of FIGS. 2 through 4 according to an embodiment of the presentdisclosure shown with a portion of the thermally-sensitive medium ofFIG. 5 associated therewith;

FIGS. 7 and 8 are partial, enlarged views schematically illustrating thethermally-sensitive medium of FIG. 5 and the energy applicator of FIG. 4centrally aligned with the longitudinal axis of the thermally-sensitivemedium's cut-out portion according to an embodiment of the presentdisclosure;

FIG. 9 is a schematic, longitudinal cross-sectional view of anembodiment of a thermal profiling system including the test fixtureassembly of FIGS. 2 through 4 and the energy applicator and thethermally-sensitive medium of FIGS. 7 and 8 in accordance with thepresent disclosure;

FIG. 10 is a schematic diagram illustrating the thermally-sensitivemedium of the thermal profiling system of FIG. 9 during operationaccording to an embodiment of the present disclosure shown with aschematically-illustrated representation of a thermal radiation patternformed on the thermally-sensitive medium at time t equal to t₁;

FIG. 11 is a schematic diagram illustrating a thresholded pattern imageof a portion of the thermally-sensitive medium of FIG. 10 showing aselected temperature band at time t equal to t₁ according to anembodiment of the present disclosure;

FIG. 12 is a schematic diagram illustrating the thermally-sensitivemedium of the thermal profiling system of FIG. 9 during operationaccording to an embodiment of the present disclosure shown with aschematically-illustrated representation of a thermal radiation patternformed on the thermally-sensitive medium at time t equal to t₂;

FIG. 13 is a schematic diagram illustrating a thresholded pattern imageof a portion of the thermally-sensitive medium of FIG. 12 showing aselected temperature band captured at time t equal to t₂ according to anembodiment of the present disclosure;

FIG. 14 is a schematic diagram illustrating the thermally-sensitivemedium of the thermal profiling system of FIG. 9 during operationaccording to an embodiment of the present disclosure shown with aschematically-illustrated representation of a thermal radiation patternformed on the thermally-sensitive medium at time t equal to t₃;

FIG. 15 is a schematic diagram illustrating a thresholded pattern imageof a portion of the thermally-sensitive medium of FIG. 14 showing aselected temperature band at time t equal to t₃ according to anembodiment of the present disclosure;

FIG. 16A is a schematic diagram illustrating a thresholded pattern imageof a thermally-sensitive medium according to an embodiment of thepresent disclosure showing a selected temperature band at time t equalto t_(n);

FIG. 16B is a schematic view of the thresholded pattern image of FIG.16A shown with contour lines at the inner and outer boundaries of thetemperature band;

FIG. 17A is a schematic diagram illustrating a thresholded pattern imageof a thermally-sensitive medium according to an embodiment of thepresent disclosure showing a selected temperature band at time t equalto t_(n+1);

FIG. 17B is a schematic view of the thresholded pattern image of FIG.17A shown with contour lines connecting a set of points at the inner andouter boundaries of the temperature band;

FIGS. 18 and 19 are schematic diagrams illustrating the positionalrelationship between points lying on the boundary lines of thetemperature band of FIGS. 16B and 17B according to an embodiment of thepresent disclosure;

FIG. 20 is a diagrammatic representation of a simulated radiationpattern for an energy applicator according to an embodiment of thepresent disclosure;

FIG. 21 is a diagrammatic representation of a simulated radiationpattern for an energy applicator according to another embodiment of thepresent disclosure;

FIG. 22 is a flowchart illustrating methods of controlling output of anelectrosurgical power generating source according to embodiments of thepresent disclosure;

FIG. 23 is a flowchart illustrating a method of controlling output of anelectrosurgical power generating source according to an embodiment ofthe present disclosure;

FIG. 24 is a flowchart illustrating a sequence of method steps forperforming the step 2360 of the method illustrated in FIG. 23 accordingto an embodiment of the present disclosure;

FIG. 25 is a schematic diagram of an ablation system including anelectrosurgical device according to an embodiment of the presentdisclosure;

FIG. 26 is a schematic diagram of the electrosurgical device of FIG. 25shown with indicia graduation marks and an indicia alignment markaccording to an embodiment of the present disclosure; and

FIGS. 27 and 28 are schematically-illustrated representations ofsimulation results showing broadside radiation patterns according toembodiments of the present disclosure.

DETAILED DESCRIPTION

Hereinafter, embodiments of the system and method for specificabsorption rate (SAR) measurement and characterization ofenergy-delivery devices of the present disclosure and embodiments of thepresently disclosed electrosurgical system and methods for controllingoutput of an electrosurgical power generating source are described withreference to the accompanying drawings. Like reference numerals mayrefer to similar or identical elements throughout the description of thefigures. As shown in the drawings and as used in this description, andas is traditional when referring to relative positioning on an object,the term “proximal” refers to that portion of the apparatus, orcomponent thereof, closer to the user and the term “distal” refers tothat portion of the apparatus, or component thereof, farther from theuser.

This description may use the phrases “in an embodiment,” “inembodiments,” “in some embodiments,” or “in other embodiments,” whichmay each refer to one or more of the same or different embodiments inaccordance with the present disclosure. For the purposes of thisdescription, a phrase in the form “A/B” means A or B. For the purposesof the description, a phrase in the form “A and/or B” means “(A), (B),or (A and B)”. For the purposes of this description, a phrase in theform “at least one of A, B, or C” means “(A), (B), (C), (A and B), (Aand C), (B and C), or (A, B and C)”.

Electromagnetic energy is generally classified by increasing energy ordecreasing wavelength into radio waves, microwaves, infrared, visiblelight, ultraviolet, X-rays and gamma-rays. As it is used in thisdescription, “microwave” generally refers to electromagnetic waves inthe frequency range of 300 megahertz (MHz) (3×10⁸ cycles/second) to 300gigahertz (GHz) (3×10¹¹ cycles/second). As it is used in thisdescription, “ablation procedure” generally refers to any ablationprocedure, such as microwave ablation, radio frequency (RF) ablation ormicrowave ablation assisted resection. As it is used in thisdescription, “energy applicator” generally refers to any device that canbe used to transfer energy from a power generating source, such as amicrowave or RF electrosurgical generator, to tissue. As it is used inthis description, “transmission line” generally refers to anytransmission medium that can be used for the propagation of signals fromone point to another.

As it is used in this description, “length” may refer to electricallength or physical length. In general, electrical length is anexpression of the length of a transmission medium in terms of thewavelength of a signal propagating within the medium. Electrical lengthis normally expressed in terms of wavelength, radians or degrees. Forexample, electrical length may be expressed as a multiple orsub-multiple of the wavelength of an electromagnetic wave or electricalsignal propagating within a transmission medium. The wavelength may beexpressed in radians or in artificial units of angular measure, such asdegrees. The electric length of a transmission medium may be expressedas its physical length multiplied by the ratio of (a) the propagationtime of an electrical or electromagnetic signal through the medium to(b) the propagation time of an electromagnetic wave in free space over adistance equal to the physical length of the medium. The electricallength is in general different from the physical length. By the additionof an appropriate reactive element (capacitive or inductive), theelectrical length may be made significantly shorter or longer than thephysical length.

As used in this description, the term “real-time” means generally withno observable latency between data processing and display. As used inthis description, “near real-time” generally refers to a relativelyshort time span between the time of data acquisition and display.

Various embodiments of the present disclosure provide systems andmethods of directing energy to tissue in accordance with specificabsorption rate data associated with an energy applicator. Embodimentsmay be implemented using electromagnetic radiation at microwavefrequencies or at other frequencies. An electromagnetic energy deliverydevice including an energy applicator array, according to variousembodiments, is designed and configured to operate between about 300 MHzand about 10 GHz.

Various embodiments of the presently disclosed electrosurgical systemincluding an energy applicator, or energy applicator array, are suitablefor microwave ablation and for use to pre-coagulate tissue for microwaveablation assisted surgical resection. In addition, although thefollowing description describes the use of a dipole microwave antenna,the teachings of the present disclosure may also apply to a monopole,helical, or other suitable type of microwave antenna (or RF electrodes).

An electrosurgical system 100 according to an embodiment of the presentdisclosure is shown in FIG. 1 and includes an electromagnetic energydelivery device or energy applicator array “E”. Energy applicator array“E” may include one or more energy applicators or probes. Probethickness may be minimized, e.g., to reduce trauma to the surgical siteand facilitate accurate probe placement to allow surgeons to treattarget tissue with minimal damage to surrounding healthy tissue. In someembodiments, the energy applicator array “E” includes a plurality ofprobes. The probes may have similar or different diameters, may extendto equal or different lengths, and may have a distal end with a taperedtip. In some embodiments, the one or more probes may be provided with acoolant chamber. The probe(s) may be integrally associated with a hub(e.g., hub 34 shown in FIG. 1) that provides electrical and/or coolantconnections to the probe(s). Additionally, or alternatively, theprobe(s) may include coolant inflow and outflow ports to facilitate theflow of coolant into, and out of, the coolant chamber. Examples ofcoolant chamber and coolant inflow and outflow port embodiments aredisclosed in commonly assigned U.S. patent application Ser. No.12/401,268 filed on Mar. 10, 2009, entitled “COOLED DIELECTRICALLYBUFFERED MICROWAVE DIPOLE ANTENNA”, and U.S. Pat. No. 7,311,703,entitled “DEVICES AND METHODS FOR COOLING MICROWAVE ANTENNAS”.

In the embodiment shown in FIG. 1, the energy applicator array “E”includes three probes 1, 2 and 3 having different lengths and arrangedsubstantially parallel to each other. Probes 1, 2 and 3 generallyinclude a radiating section “R1”, “R2” and “R3”, respectively, operablyconnected by a feedline (or shaft) 1 a, 2 a and 3 a, respectively, to anelectrosurgical power generating source 16, e.g., a microwave or RFelectrosurgical generator. Transmission lines 10, 11 and 12 may beprovided to electrically couple the feedlines 1 a, 2 a and 3 a,respectively, to the electrosurgical power generating source 16. Locatedat the distal end of each probe 1, 2 and 3 is a tip portion 1 b, 2 b and3 b, respectively, which may be configured to be inserted into an organ“OR” of a human body or any other body tissue. Tip portion 1 b, 2 b and3 b may terminate in a sharp tip to allow for insertion into tissue withminimal resistance. Tip portion 1 b, 2 b and 3 b may include othershapes, such as, for example, a tip that is rounded, flat, square,hexagonal, or cylindroconical. The shape, size and number of probes ofthe energy applicator array “E” may be varied from the configurationdepicted in FIG. 1.

Electrosurgical system 100 according to embodiments of the presentdisclosure includes a user interface 50 may include a display device 21,such as without limitation a flat panel graphic LCD (liquid crystaldisplay), adapted to visually display one or more user interfaceelements (e.g., 23, 24 and 25 shown in FIG. 1). In an embodiment, thedisplay device 21 includes touchscreen capability, e.g., the ability toreceive user input through direct physical interaction with the displaydevice 21, e.g., by contacting the display panel of the display device21 with a stylus or fingertip. A user interface element (e.g., 23, 24and/or 25 shown in FIG. 1) may have a corresponding active region, suchthat, by touching the display panel within the active region associatedwith the user interface element, an input associated with the userinterface element is received by the user interface 50.

User interface 50 may additionally, or alternatively, include one ormore controls 22 that may include without limitation a switch (e.g.,pushbutton switch, toggle switch, slide switch) and/or a continuousactuator (e.g., rotary or linear potentiometer, rotary or linearencoder). In an embodiment, a control 22 has a dedicated function, e.g.,display contrast, power on/off, and the like. Control 22 may also have afunction that may vary in accordance with an operational mode of theelectrosurgical system 100. A user interface element (e.g., 23 shown inFIG. 1) may be provided to indicate the function of the control 22.Control 22 may also include an indicator, such as an illuminatedindicator, e.g., a single- or variably-colored LED (light emittingdiode) indicator.

In some embodiments, the electrosurgical power generating source 16 isconfigured to provide microwave energy at an operational frequency fromabout 300 MHz to about 2500 MHz. In other embodiments, the powergenerating source 16 is configured to provide microwave energy at anoperational frequency from about 300 MHz to about 10 GHz. Powergenerating source 16 may be configured to provide various frequencies ofelectromagnetic energy.

Feedlines 1 a, 2 a and 3 a may be formed from a suitable flexible,semi-rigid or rigid microwave conductive cable, and may connect directlyto an electrosurgical power generating source 16. Feedlines 1 a, 2 a and3 a may have a variable length from a proximal end of the radiatingsections “R1”, “R2” and “R3”, respectively, to a distal end of thetransmission lines 10, 11 and 12, respectively, ranging from a length ofabout one inch to about twelve inches. Feedlines 1 a, 2 a and 3 a may bemade of stainless steel, which generally offers the strength required topuncture tissue and/or skin. Feedlines 1 a, 2 a and 3 a may include aninner conductor, a dielectric material coaxially surrounding the innerconductor, and an outer conductor coaxially surrounding the dielectricmaterial. Radiating sections “R1”, “R2” and “R3” may be formed from aportion of the inner conductor that extends distal of the feedlines 1 a,2 a and 3 a, respectively, into the radiating sections “R1”, “R2” and“R3”, respectively. Feedlines 1 a, 2 a and 3 a may be cooled by fluid,e.g., saline, water or other suitable coolant fluid, to improve powerhandling, and may include a stainless steel catheter. Transmission lines10, 11 and 12 may additionally, or alternatively, provide a conduit (notshown) configured to provide coolant fluid from a coolant source 32 tothe energy applicator array “E”.

As shown in FIG. 1, the electrosurgical system 100 may include areference electrode 19 (also referred to herein as a “return”electrode). Return electrode 19 may be electrically coupled via atransmission line 20 to the power generating source 16. During aprocedure, the return electrode 19 may be positioned in contact with theskin of the patient or a surface of the organ “OR”. When the surgeonactivates the energy applicator array “E”, the return electrode 19 andthe transmission line 20 may serve as a return current path for thecurrent flowing from the power generating source 16 through the probes1, 2 and 3.

During microwave ablation, e.g., using the electrosurgical system 100,the energy applicator array “E” is inserted into or placed adjacent totissue and microwave energy is supplied thereto. Ultrasound or computedtomography (CT) guidance may be used to accurately guide the energyapplicator array “E” into the area of tissue to be treated. Probes 1, 2and 3 may be placed percutaneously or surgically, e.g., usingconventional surgical techniques by surgical staff. A clinician maypre-determine the length of time that microwave energy is to be applied.Application duration may depend on a variety of factors such as energyapplicator design, number of energy applicators used simultaneously,tumor size and location, and whether the tumor was a secondary orprimary cancer. The duration of microwave energy application using theenergy applicator array “E” may depend on the progress of the heatdistribution within the tissue area that is to be destroyed and/or thesurrounding tissue.

FIG. 1 shows a targeted region including ablation targeted tissuerepresented in sectional view by the solid line “T”. It may be desirableto ablate the targeted region “T” by fully engulfing the targeted region“T” in a volume of lethal heat elevation. Targeted region “T” may be,for example, a tumor that has been detected by a medical imaging system30.

Medical imaging system 30, according to various embodiments, includes ascanner (e.g., 15 shown in FIG. 1) of any suitable imaging modality, orother image acquisition device capable of generating input pixel datarepresentative of an image, e.g., a digital camera or digital videorecorder. Medical imaging system 30 may additionally, or alternatively,include a medical imager operable to form a visible representation ofthe image based on the input pixel data. Medical imaging system 30 mayinclude a storage device such as an internal memory unit, which mayinclude an internal memory card and removable memory. In someembodiments, the medical imaging system 30 may be a multi-modal imagingsystem capable of scanning using different modalities. Examples ofimaging modalities that may be suitably and selectively used includeX-ray systems, ultrasound (UT) systems, magnetic resonance imaging (MRI)systems, computed tomography (CT) systems, single photon emissioncomputed tomography (SPECT), and positron emission tomography (PET)systems. Medical imaging system 30, according to embodiments of thepresent disclosure, may include any device capable of generating digitaldata representing an anatomical region of interest. Medical imagingsystem 30 may be a multi-modal imaging system capable of scanning tissuein a first modality to obtain first modality data and a second modalityto obtain second modality data, wherein the first modality data and/orthe second modality data includes tissue temperature information. Thetissue temperature information acquired by the one or more imagingmodalities may be determined by any suitable method, e.g., calculatedfrom density changes within the tissue.

Image data representative of one or more images may be communicatedbetween the medical imaging system 30 and a processor unit 26. Medicalimaging system 30 and the processor unit 26 may utilize wiredcommunication and/or wireless communication. Processor unit 26 mayinclude any type of computing device, computational circuit, or any typeof processor or processing circuit capable of executing a series ofinstructions that are stored in a memory (not shown) associated with theprocessor unit 26. Processor unit 26 may be adapted to run an operatingsystem platform and application programs. Processor unit 26 may receiveuser inputs from a keyboard (not shown), a pointing device 27, e.g., amouse, joystick or trackball, and/or other device communicativelycoupled to the processor unit 26.

A scanner (e.g., 15 shown in FIG. 1) of any suitable imaging modalitymay additionally, or alternatively, be disposed in contact with theorgan “OR” to provide image data. As an illustrative example, the twodashed lines 15A in FIG. 1 bound a region for examination by the scanner15, e.g., a real-time ultrasonic scanner.

In FIG. 1, the dashed line 8 surrounding the targeted region “T”represents the ablation isotherm in a sectional view through the organ“OR”. Such an ablation isotherm may be that of the surface achievingpossible temperatures of approximately 50° C. or greater. The shape andsize of the ablation isotherm volume, as illustrated by the dashed line8, may be influenced by a variety of factors including the configurationof the energy applicator array “E”, the geometry of the radiatingsections “R1”, “R2” and “R3”, cooling of the probes 1, 2 and 3, ablationtime and wattage, and tissue characteristics. Processor unit 26 may beconnected to one or more display devices (e.g., 21 shown in FIG. 1) fordisplaying output from the processor unit 26, which may be used by theclinician to visualize the targeted region “T” and/or the ablationisotherm volume 8 in real-time or near real-time during a procedure,e.g., an ablation procedure.

In embodiments, real-time data and/or near real-time data acquired fromCT scan, ultrasound, or MRI (or other scanning modality) that includestissue temperature information may be outputted from the processor unit26 to one or more display devices. Processor unit 26 is adapted toanalyze image data including tissue temperature information to determinea specific absorption rate (SAR) around an energy applicator as afunction of the tissue temperature information obtained from the imagedata. A possible advantage to taking SAR directly from the patient isthat any tissue inconsistencies in the local area of the antenna orelectrode would be detected using this SAR. Calculating SAR from theelectrode or antenna as it is being used in the patient may allowdetection of the beginning of a non-uniform ablation field.

In some embodiments, the patient's anatomy may be scanned by one or moreof several scanning modalities, such as CT scanning, MRI scanning,ultrasound, PET scanning, etc., so as to visualize the tumor and thesurrounding normal tissue. The tumor dimensions may thereby bedetermined and/or the location of the tumor relative to criticalstructures and the external anatomy may be ascertained. An optimalnumber and size of energy applicators might be selected so that theablation isotherms can optimally engulf and kill the tumor with aminimal number of electrode insertions and minimal damage to surroundinghealthy tissue.

Electrosurgical system 100 may include a library 200 including aplurality of thermal profiles or overlays 202-202 _(n). As it is used inthis description, “library” generally refers to any repository,databank, database, cache, storage unit and the like. Each of theoverlays 202-202 may include a thermal profile that is characteristic ofand/or specific to a particular energy applicator design, particularenergy applicator array, and/or exposure time. Examples of overlayembodiments are disclosed in commonly assigned U.S. patent applicationSer. No. 11/520,171 filed on Sep. 13, 2006, entitled “PORTABLE THERMALLYPROFILING PHANTOM AND METHOD OF USING THE SAME”, and U.S. patentapplication Ser. No. 11/879,061 filed on Jul. 16, 2007, entitled “SYSTEMAND METHOD FOR THERMALLY PROFILING RADIOFREQUENCY ELECTRODES”, thedisclosures of which are incorporated herein by reference in theirentireties.

Library 200 according to embodiments of the present disclosure mayinclude a database 284 that is configured to store and retrieve energyapplicator data, e.g., parameters associated with one or energyapplicators (e.g., 1, 2 and 3 shown in FIG. 1) and/or one or more energyapplicator arrays (e.g., “E” shown in FIG. 1). Parameters stored in thedatabase 284 in connection with an energy applicator, or an energyapplicator array, may include, but are not limited to, energy applicator(or energy applicator array) identifier, energy applicator (or energyapplicator array) dimensions, a frequency, an ablation length (e.g., inrelation to a radiating section length), an ablation diameter, atemporal coefficient, a shape metric, and/or a frequency metric. In anembodiment, ablation pattern topology may be included in the database284, e.g., a wireframe model of an energy applicator array (e.g., 25shown in FIG. 1) and/or a representation of a radiation patternassociated therewith.

Library 200 according to embodiments of the present disclosure may be incommunicatively associated with a picture archiving and communicationsystem (PACS) database (shown generally as 58 in FIG. 1), e.g.,containing DICOM (acronym for Digital Imaging and Communications inMedicine) formatted medical images. PACS database 58 may be configuredto store and retrieve image data including tissue temperatureinformation. As shown in FIG. 1, the processor unit 26 may becommunicatively associated with the PACS database 58. In accordance withone or more presently-disclosed methods, image data associated with aprior treatment of a target tissue volume is retrieved from the PACSdatabase 58 (e.g., step 2245 shown in FIG. 22), and the SAR iscalculated as a function of the tissue temperature information from theimage data (e.g., step 2260 shown in FIG. 22).

Images and/or non-graphical data stored in the library 200, and/orretrievable from the PACS database 58, may be used to configure theelectrosurgical system 100 and/or control operations thereof. Forexample, thermal profiling data associated with an energy applicator,according to embodiments of the present disclosure, may be used as afeedback tool to control an instrument's and/or clinician's motion,e.g., to allow clinicians to avoid ablating critical structures, such aslarge vessels, healthy organs or vital membrane barriers.

Images and/or non-graphical data stored in the library 200, and/orretrievable from the PACS database 58, may be used to facilitateplanning and effective execution of a procedure, e.g., an ablationprocedure. Thermal profile data associated with an energy applicator,according to embodiments of the present disclosure, may be used as apredictive display of how an ablation will occur prior to the process ofablating. Thermal profile data associated with an energy applicator,according to embodiments of the present disclosure, may be used todetermine a specific absorption rate (SAR) around the energy applicator.A simulated radiation pattern for the energy applicator may be generatedas a function of the SAR around the energy applicator. For example, thePennes' bio-heat equation coupled with electrical field equations in afinite element analysis (FEA) environment generally provides a governingstructure for computer simulations modeling energy deposition inbiological tissues. It is envisioned and within the scope of the presentdisclosure that the Pennes' bio-heat equation coupled with electricalfield equations in a FEA environment may be used to generate simulatedradiation patterns for an energy applicator as a function of the SARaround the energy applicator. Images, simulated radiation patterns(e.g., “P1” and “P2” shown in FIGS. 20 and 21, respectively) and/orinformation displayed on the display device 21 of the user interface 50,for example, may be used by the clinician to better visualize andunderstand how to achieve more optimized results during thermaltreatment of tissue, such as, for example, ablation of tissue, tumorsand cancer cells.

An embodiment of a system (shown generally as 900 in FIG. 9) suitablefor specific absorption rate measurement and characterization ofenergy-delivery devices in accordance with the present disclosureincludes the test fixture assembly 300 of FIGS. 2 through 4, athermally-sensitive, color-changing medium (e.g., 331 shown in FIGS. 3and 4) disposed within the test fixture assembly 300, and may include ahydrogel material 304 disposed around the thermally-sensitive medium.Test fixture assembly 300 includes a housing 302 including a wall 302 a,a port 303 defined in the wall 302 a, and a support member 325 adaptedto support at least a portion of a thermally-sensitive, color-changingmedium disposed within an interior area (shown generally as 301 in FIG.2) of the housing 302. The thermally-sensitive, color-changing mediummay be a sheet or layer of thermally-sensitive paper or film, may have asingle- or multi-layer structure, and may include a supportingsubstrate. A layer of a thermally-sensitive medium may be composed ofdifferent materials.

Housing 302 may be configured to contain a quantity of a fluid and/orgel material 304, e.g., an electrically and thermally conductivepolymer, hydrogel, or other suitable transparent orsubstantially-transparent medium having electrical and thermalconductivity. Housing 302 includes a bottom portion 315 and a wall 302 aextending upwardly from the bottom portion 315 to define an interiorarea or space (e.g., 301 shown in FIG. 2). Housing 302 may be fabricatedfrom any suitable material, e.g., plastic or other moldable material,and may have a substantially rectangular or box-like shape. Inembodiments, the housing 302 may include an electrically non-conductivematerial, e.g., plastics, such as polyethylene, polycarbonate, polyvinylchloride (PVC), or the like. Housing 302 may be fabricated from metals,plastics, ceramics, composites, e.g., plastic-metal or ceramic-metalcomposites, or other materials. In some embodiments, the housing 302 isformed of a high thermal conductivity material, e.g., aluminum. Theshape and size of the housing 302 may be varied from the configurationdepicted in FIGS. 2 through 4. Housing 302 may have the differentanatomical shapes, such as, for example, circular, ovular,kidney-shaped, liver-shaped, or lung shaped, which may allow a clinicianto better visualize the potential effects of thermal treatment on apatient prior to actually performing the treatment procedure.

Housing 302, according to embodiments of the present disclosure,includes one or more ports (e.g., 303 shown in FIG. 3) defined in thehousing 302 and configured to allow at least a distal portion of a probe(shown generally as 1 in FIGS. 1, 4, 7, 8 and 9) to be disposed in aninterior area of the housing 302. The port(s) may be configured toaccommodate different size probes.

As shown in FIG. 3, a fixture or fitting 306 may be provided to the port303. Fitting 306 may be configured to extend through a wall 302 a of thehousing 302. Fitting 306 generally includes a tubular portion (e.g., 307shown in FIG. 3) defining a passageway (e.g., 308 shown in FIG. 2)configured to selectively receive a probe (e.g., 1 shown in FIG. 4)therethrough. In embodiments, the fitting 306 may be configured toinhibit leakage of the hydrogel 304 from within the housing 302, e.g.,when the probe is removed from the fitting 306. Fitting 306 mayadditionally, or alternatively, form a substantially fluid tight sealaround the probe when the probe is inserted therethrough. Fitting 306may be a single-use fitting. Fitting 306 may be replaceable after eachuse or after several uses. Fitting 306 may include, but is not limitedto, a luer-type fitting, a pierceable membrane port, and the like.Guards 306 a may be disposed on opposite sides of the fitting 306 toprevent inadvertent contact or disruption of the fitting 306. Testfixture assembly 300, according to embodiments of the presentdisclosure, may include a plurality of ports defined in the housing 302,e.g., to accommodate multiple probes. Test fixture assembly 300 mayadditionally, or alternatively, include a plurality of fittings 306.

In some embodiments, the test fixture assembly 300 includes a groundring 310 disposed within the housing 302. Ground ring 310 may includeany suitable electrically-conductive material, e.g., metal such asaluminum. During operation of the thermal profiling system 900, theground ring 310 may receive and/or transmit electromagnetic energyfrom/to an energy applicator associated with the test fixture assembly300. As shown in FIGS. 2 and 3, the ground ring 310 may have a shapethat substantially complements the shape of the housing 302, e.g., toextend substantially around an inner perimeter of the housing 302. Aground connection 312 may be provided that is adapted to electricallyconnect to the ground ring 310. As shown in FIGS. 3 and 4, the groundconnection 312 may extend through a wall of the housing 302, and may beused to electrically connect the ground ring 310 to an electrosurgicalpower generating source (e.g., 16 shown in FIG. 9). In some embodiments,the ground ring 310 may be removable. The ground ring 310 may be removedin order to reduce any reflected energy that may be caused by thepresence of the ground ring 310, which may be influenced by probeconfiguration and operational parameters. For example, it may bedesirable to remove the ground ring 310 when microwave operationalfrequencies are used.

Test fixture assembly 300 according to embodiments of the presentdisclosure includes a support member 325 disposed on and extendinginwardly from an inner surface of a wall 302 a of the housing 302, andmay include at least one support rod 322 extending upwardly into thehousing 302 from a lower surface thereof. FIG. 6 shows an embodiment ofthe support member 325 that includes a shelf portion 320, a recess inthe form of a groove 320 a defined in the planar top surface “S” of theshelf portion 320, and a shelf support member 328 coupled to the shelfportion 320. Shelf portion 320 and the shelf support member 328 may beintegrally formed. As shown in FIG. 6, a channel 328 a is defined in theshelf support member 328 and extends therethrough. In some embodiments,the channel 328 a has a substantially cylindrical shape and the groove320 a has a substantially half-cylindrical shape, and the groove 320 amay be substantially aligned with a lower, half-cylindrical portion ofthe channel 328 a.

FIG. 9 shows an embodiment of a thermal profiling system 900 accordingto the present disclosure that includes the test fixture assembly 300 ofFIGS. 2 through 4 and an imaging system 918. Imaging system 918 includesan image acquisition unit 912 capable of generating image data, and mayinclude an image processing unit 954 in communication with the imageacquisition unit 912. Image acquisition unit 912 may include anysuitable device capable of generating input pixel data representative ofan image, e.g., a digital camera or digital video recorder. An image mayhave 5120 scan lines, 4096 pixels per scan lines and eight bits perpixel, for example. As described in more detail herein, at least onesheet or layer of a suitable thermally-sensitive medium 331 is disposedwithin an interior area (shown generally as 301 in FIG. 2) of thehousing 302. Image acquisition unit 912, according to embodiments to thepresent disclosure, is configured to capture time-series image data ofthermal radiation patterns formed on the thermally-sensitive medium 331,and may be disposed over the interior area of the housing 302 orotherwise suitably positioned to facilitate image capture of thethermally-sensitive medium 331, or portion thereof.

In some embodiments, the thermally-sensitive medium 331 may includeliquid crystal (LC) thermometry paper. A plurality of sheets of thethermally-sensitive medium 331 may be provided to generate a set ofthermal profiles thereon in accordance with characteristics of an energyapplicator and/or parameters and/or settings of a power generatingsource. The shape, size and number of sheets of the thermally-sensitivemedium 331 may be varied from the configuration depicted in FIGS. 3 and4. In some embodiments, the thermally-sensitive medium 331 may have ashape that conforms to the shape of the selected housing (e.g., 302shown in FIGS. 2 through 4) and/or the thermally-sensitive medium 331may be shaped to allow circulation of a heated medium, e.g., hydrogel,thereabout.

Thermal profiling system 900 may include an electrosurgical powergenerating source 16. As shown in FIG. 9, the feedline 1 a of the energyapplicator 1 associated with the test fixture assembly 300 may beelectrically coupled to an active port or terminal of theelectrosurgical power generating source 16, and the ground connection321 of the test fixture assembly 300 may be electrically coupled to areturn port or terminal of the power generating source 16.

Thermal profiling system 900, according to embodiments of the presentdisclosure, may include a temperature control unit (not shown) capableof detecting the temperature of the hydrogel 304 and maintaining thehydrogel 304 at a predetermined temperature or temperature range. Inaccordance with embodiments of the present disclosure, the differencebetween the ambient temperature of the hydrogel 304 and the thresholdtemperature of the thermally-sensitive medium 331 is designed to berelatively small, e.g., to allow close to adiabatic conditions. Forexample, the thermal profiling system 900 may be configured to maintainthe hydrogel 304 at a temperature of about 34.5° C., and thethermally-sensitive medium 331 may be selected to have a thresholdtemperature of about 35.0° C.

Thermally-sensitive medium 331 according to embodiments of the presentdisclosure includes a cut-out portion (e.g., 332 shown in FIG. 5)defining a void in the thermally-sensitive medium 331. The cut-outportion may be configured to substantially match the profile of anenergy applicator, and may be configured to provide a gap (e.g., “G”shown in FIG. 7) between the energy applicator and thethermally-sensitive medium 331 at the edge of the cut-out portion.Thermally-sensitive medium 331 may have any suitable thermalsensitivity. In some embodiments, the thermally-sensitive medium 331 hasa thermal sensitivity of about one degree Celsius. Thermally-sensitivemedium 331, or portion thereof, may be disposed over at least a portionof the support member 325. Additionally, or alternatively, at least aportion of the thermally-sensitive medium 331 may be disposed over oneor more support rods 322.

In some embodiments, at least a portion of the thermally-sensitivemedium 331 is disposed over the shelf portion 320 and positioned tosubstantially align a longitudinal axis (e.g., “A-A” shown in FIG. 5) ofa cut-out portion 332 with a central longitudinal axis (e.g., “A-A”shown in FIG. 6) of the channel 328 a of the shelf support member 328.In some embodiments, a longitudinal axis (e.g., “A-A” shown in FIG. 5)of the cut-out portion 332 is arranged parallel to the centrallongitudinal axis (e.g., “A-A” shown in FIG. 6) of the channel 328 a. Ascooperatively shown in FIGS. 3 and 9, a fitting 306 may be provided tothe port 303 defined in the wall 302 a of the housing 302, wherein atubular portion 307 of the fitting 306 may be configured to extendthrough the port 303 and into the channel 328 a of the support member325. Tubular portion 307 disposed within the port 303 and channel 328 amay help to maintain alignment of the energy applicator (e.g., 1 shownin FIGS. 4 and 9) with respect to the cut-out portion 332 of thethermally-sensitive medium 331. Fitting 307 may be provided with asleeve member (e.g., 308 a shown in FIG. 4) substantially coaxiallyaligned with the tubular portion 307, e.g., to provide a resilientlycompressible seal around an energy applicator portion disposed therein.The sleeve member may be formed of a compliant material, e.g., silicon,natural or synthetic rubber, or other suitable resiliently compressiblematerial.

In some embodiments, the shelf portion 320 and one or more support rods322 function to support a thermally-sensitive medium 331 within thehousing 302. Shelf portion 320 and the support rod(s) 322, according toembodiments of the present disclosure, may be configured to support thethermally-sensitive medium 331 such that the thermally-sensitive medium331 is maintained in a plane (e.g., “P” shown in FIG. 5) substantiallyparallel to a facing surface of the bottom portion 315 of the housing302. Shelf portion 320 and the support rod(s) 322 may additionally, oralternatively, be configured to support the thermally-sensitive medium331 such that the thermally-sensitive medium 331 is maintained in aplane substantially parallel to a plane of the shelf portion 320. Shelfportion 320 and the support rod(s) 322 may additionally, oralternatively, be configured to support the thermally-sensitive medium331 such that a longitudinal axis (e.g., “A-A” shown in FIG. 5) of thecut-out portion 332 is substantially aligned with the centrallongitudinal axis (e.g., “A-A” shown in FIG. 8) of an energy applicator(e.g., 1 shown in FIG. 8) associated therewith.

Thermal profiling system 900, according to embodiments of the presentdisclosure, includes a transparent housing portion (e.g., “W” shown inFIG. 4) for providing viewing into the interior area of the housing 302,and may include a cover 340 configured to selectively overlie thehousing 302. Cover 340, or portion thereof, may be fabricated from anysuitable transparent or substantially transparent material, e.g., glass,optically transparent thermoplastics, such as polyacrylic orpolycarbonate. In some embodiments, the housing 302 includes a top edgeportion (e.g., 339 shown in FIG. 2), which can take any suitable shape.Cover 340 may be releaseably securable to a top edge portion of thehousing 302 by any suitable fastening element, e.g., screws, bolts,pins, clips, clamps, and hinges.

As shown in FIG. 9, the thermal profiling system 900 includes an imagingsystem 918 operatively associated with the electrosurgical powergenerating source 916 and the housing 302, and may include a displaydevice 21 electrically coupled to the electrosurgical power generatingsource 916. For example, the imaging system 918 may include an imageacquisition unit 912 for recording the visual changes occurring inthermally-sensitive medium 331 and/or parameters and/or settings of theelectrosurgical power generating source 916 (e.g., power settings, timesettings, wave settings, duty-cycle settings, energy applicator 1configuration, etc.). Imaging system 918 may be communicatively coupledto a PACS database (e.g., 58 shown in FIG. 1). Imaging system 918 mayalso include an image processing unit 954 to which a portable storagemedium 958 may be electrically connected. Portable storage medium 958may, among other things, allow for transfer of image data in DICOMformat to a PACS database (e.g., 58 shown in FIG. 1). As shown in FIG.9, the image processing unit 954 is electrically connected between theimage acquisition unit 912 and the power generating source 916, and maybe electrically connected to the display device 21.

Hereinafter, a method of measuring specific absorption rate andcharacterizing an energy applicator using a thermal phantom and imageanalysis in accordance with the present disclosure is described withreference to FIGS. 1 through 9. Test fixture assembly 300 of FIGS. 2through 4 is provided, and a hydrogel material 304 is introduced intothe interior area 301 of the housing 302 of the test fixture assembly300. A thermally-sensitive medium 331 including a cut-out portion 332 isplaced into the housing 302 containing hydrogel 304 therein, e.g., insuch a manner that a color changing side of the thermally-sensitivemedium 331 is facing the cover 340 or away from the bottom portion 315.Thermally-sensitive medium 331 may be positioned within the housing 302such that at least a portion of thermally-sensitive medium 331 is placedon the shelf portion 320 of the support member 325 and/or at least aportion of thermally-sensitive medium 331 is placed on support rods 322.In one embodiment, fasteners, such as screws, may be used to secure thethermally-sensitive medium 331 to the shelf portion 320 and/or thesupport rods 322. With the thermally-sensitive medium 331 submerged inhydrogel 304 within the housing 302, the cover 340 may be secured to thehousing 302, e.g., to substantially enclose the thermally-sensitivemedium 331 within the housing 302.

The selected energy applicator (e.g., 1 shown in FIGS. 1, 4 and 9) isintroduced into the housing 302 through the port 303 by placing a distaltip portion (e.g., 1 b shown in FIG. 1) into a fitting 306 disposedtherein and advancing the energy applicator therethrough until at leasta portion of the radiating section of the energy applicator is locatedwith the cut-out portion 332 of the thermally-sensitive medium 331. Asshown in FIG. 7, the energy applicator 1 disposed in the cut-out portion332 may be spaced apart a distance or gap “G” from thethermally-sensitive medium 331. Gap “G” may be configured to be asnarrow a distance as can be achieved, without making contact between thethermally-sensitive medium 331 and the energy applicator 1. In someembodiments, the gap “G” may be about 1 millimeter. As shown in FIG. 7,the width of the gap “G” may be substantially the same around the entireperiphery of the energy applicator 1, e.g., to minimize errors in theimage processing and analysis stage.

Energy applicator 1 is electrically connected to an active port orterminal of electrosurgical power generating source 916, and the groundconnection 312 of the test fixture assembly 300 is electricallyconnected to a return port or terminal of power generating source 916.Test fixture assembly 300, according to embodiments of the presentdisclosure, is adapted to maintain the position of at least a distalportion of the energy applicator 1 disposed within the test fixtureassembly 300 such that the central longitudinal axis (e.g., “A-A” shownin FIG. 8) of the energy applicator 1 is substantially parallel to aplane (e.g., “P” shown in FIG. 5) containing the thermally-sensitivemedium 331.

In some embodiments, the power generating source 916 is configured orset to a predetermined setting. For example, power generating source 916may be set to a predetermined temperature, such as a temperature thatmay be used for the treatment of pain (e.g., about 42° C. or about 80°C.), a predetermined waveform, a predetermined duty cycle, apredetermined time period or duration of activation, etc.

When the energy applicator 1 is positioned within the test fixtureassembly 300, the imaging system 918 may be activated to record anyvisual changes in the thermally-sensitive medium 331, the settingsand/or parameters of the power generating source 916, and theconfiguration of the energy applicator 1.

According to an embodiment of the present disclosure, prior toactivation of the electrosurgical power generating source 916, atemperature of the hydrogel 304 within the housing 302 is stabilized toa temperature of approximately 37° C. When the power generating source916 is activated, electromagnetic energy communicated between theradiating section (e.g., “R1” shown in FIG. 4) of the energy applicator1 and ground ring 310 affects the thermally-sensitive medium 331 tocreate a thermal image (e.g., “S1” shown in FIG. 10) thereon.

The method may further include operating the imaging system 918 tocapture a time series of thermal images (e.g., “S1”, “S2” and “S3” shownin FIGS. 10, 12 and 14, respectively). For example, the temperaturegradients or “halos” created on the thermally-sensitive medium 331 maybe captured by the image acquisition unit 912 of the imaging system 918,and may be stored electronically in the image processing unit 954 or theportable storage medium 958 communicatively coupled thereto. As heatgenerated by the electromagnetic radiation emitted from energyapplicator 1 affects the thermally-sensitive medium 331, the temperaturegradients or “halos”, e.g., colored rings or bands, indicate areas ofrelatively higher temperature and areas of relatively lower temperature.It is contemplated that the particular thermally-sensitive medium 331used may be selected so as to display only a single temperature ofinterest as opposed to a range of temperatures.

Additionally, the imaging system 918 may record and store the settingsand/or parameters of the electrosurgical power generating source 916(e.g., temperature, impedance, power, current, voltage, mode ofoperation, duration of application of electromagnetic energy, etc.)associated with the creation of the image on the thermally-sensitivemedium 331.

Following the acquisition of images created on the thermally-sensitivemedium 331, the power generating source 916 may be deactivated and theenergy applicator 1 withdrawn from the housing 302. The usedthermally-sensitive medium 331 may be removed from the housing 302 andreplaced with a new or un-used thermally-sensitive medium 331. Theabove-described method may be repeated for the same or different set ofsettings and/or parameters for the power generating source 916 and/orthe same or different energy applicator 1 configuration.

Thermal profiling system 900 may be used in conjunction with anysuitable hypothermic and/or ablative energy system including, forexample, microwave energy systems employing microwave antennas fordelivering ablative energy. The above-described thermal profiling system900 has been specifically described in relation to the characterizationof a single energy applicator 1. However, it is envisioned and withinthe scope of the present disclosure that test fixture assembly 300 beconfigured to receive multiple energy applicators, e.g., two or more,and for images and/or data to be acquired thereof, in accordance withthe method described above.

During use of the thermal profiling system 900, the image acquisitionunit 912 of the imaging system 918 acquires a series of images of thethermally-sensitive medium 331 with color bands formed thereon disposedaround the energy applicator 1. Image acquisition unit 912 may acquire aseries of images with varying time delays before image acquisition. Insome embodiments, the image acquisition unit 912 acquires a time seriesof images wherein the series of images is recorded along time at uniformtime intervals.

FIGS. 10, 12 and 14 show an energy applicator 1 disposed within thecut-out portion 332 of the thermally-sensitive medium 331 withschematically-illustrated representations of thermal radiation patterns“S₁”, “S₂” and “S₃” respectively, formed on the thermally-sensitivemedium 331 during use of the thermal profiling system 900 at time tequal to t₁, t₂ and t₃, respectively. In FIGS. 10, 12 and 14, aplurality of color bands (also referred to herein as temperature bands)are shown around the energy applicator 1. The shape, size and number oftemperature bands on the thermally-sensitive medium 331 may be variedfrom the configurations depicted in FIGS. 10, 12 and 14.

Imaging system 918, according to various embodiments, includes an imageprocessing unit 954 in communication with the image acquisition unit912. A time series of image data acquired by the image acquisition unit912 (or image data from other imaging modalities such as MRI) may beinputted and stored in a memory (not shown) of the image processing unit954. According to embodiments of the present disclosure, one or moretemperature bands (e.g., “B₁”, “B₂”, “B₃” and/or “B₄” shown in FIG. 14)may be selected, either manually by the user, e.g., using a pointingdevice (e.g., 27 shown in FIG. 1) and/or the touchscreen capability of adisplay device (e.g., 21 shown in FIG. 1), or automatically, e.g., bythe image processing unit 954, for image processing to generate data foruse in characterizing the energy applicator 1.

A method according to embodiments of the present disclosure includesthresholding to segment an image data by setting all pixels whoseintensity values are above a predetermined threshold to a foregroundvalue and all the remaining pixels to a background value.

FIGS. 11, 13 and 15 show thresholded pattern images “T₁”, “T₂” and “T₃”,respectively, of a portion of the thermally-sensitive medium of FIGS.10, 12 and 14 showing a selected temperature band “B₂” at time t equalto t₁, t₂ and t₃, respectively.

A method according to embodiments of the present disclosure includesgenerating image data on the basis of thresholded pattern images of theselected temperature band (e.g., “B” shown in FIGS. 16A and 17A)surrounded by an inner boundary (e.g., “IB” shown in FIGS. 16B and 17B)and/or an outer boundary (e.g., “OB” shown in FIGS. 16B and 17B).

FIG. 16A shows a selected temperature band “B” at time t equal to t_(n),and FIG. 17B shows the temperature band “B” at time t equal to t_(n+1).As illustratively shown in FIGS. 16B and 17B, thresholding oftime-series image data may be used to detect an inner boundary and anouter boundary of the selected color band in each image data of thetime-series image data.

An example of the positional relationships between two points lying onthe boundaries of a temperature band (e.g., “B” of FIGS. 16B and 17B) isshown in FIGS. 18 and 19. For illustrative purposes, the inner and outerboundaries “L1” and “L2”, respectively, of a temperature band, at time tequal to t_(n) (shown by the solid curved lines in FIG. 18 and thedashed curved lines in FIG. 19), and at time t equal to t_(n+1) (shownby the solid curved lines in FIG. 19), are plotted on a coordinate gridhaving equal scale units “D”. In the interest of simplicity, unit “D”may be taken to be equal to the width of the cut-out portion, forillustrative purposes. It is contemplated that other spatial data orfeatures may be used to establish a measurement scale, such as gridlines or marks, or objects, placed on the thermally-sensitive mediumprior to image acquisition, or the diameter of the energy applicator.

In FIGS. 18 and 19, each of the points “P₁” and “P₂” may correspond to asingle pixel or to a group of pixels. Referring to FIG. 18, at time tequal to t_(n), the point “P₁” on the inner boundary “L1” is spacedapart a length “J” from an edge point of the cut-out portion, and thepoint “P₂” on the outer boundary “L2” is spaced apart a length “K” froman edge point of the cut-out portion. In this example, the length “J” isequal to 2 times the unit “D”. Turning now to FIG. 19, at time t equalto t_(n+1), the point “P₁” on the inner boundary “L1” is spaced apart alength “L” from a cut-out portion edge point, and the point “P₂” on theouter boundary “L2” is spaced apart a length “M” from a cut-out portionedge point. In this example, the length “L” is equal to 2.5 times theunit “D”. In the present example, it can be calculated from thecoordinate grid that, from a time t equal to t_(n) to t equal tot_(n+1), the point “P₁” on the inner boundary “L1” of the temperatureband moves, from a first position to a second position on the coordinategrid, a distance equal to one-half of the unit “D”. According to anembodiment of the present disclosure, determination of the positionalchange of point “P₁” on the inner boundary “L1” of the temperature bandprovides the value of the temperature difference, ΔT, for use incalculating the specific absorption rate. The difference in time from atime t equal to t_(n) to t equal to t_(n+1) may be set by the frame rateof the image acquisition device (e.g., 912 shown in FIG. 9).

The specific absorption rate (SAR) may be calculated by the followingequation:

$\begin{matrix}{{{SAR} = {c_{\rho}\frac{\Delta \; T}{\Delta \; t}}},} & (4)\end{matrix}$

where c_(p) is the specific heat of the hydrogel 304 (in units ofJoules/kg-° C.), ΔT is the temperature difference (° C.), and Δt is thetime period in accordance with the frame rate, or a fraction or multiplethereof, in seconds.

Hereinafter, methods of controlling output of an electrosurgical powergenerating source are described with reference to FIGS. 22 and 23. It isto be understood that the steps of the methods provided herein may beperformed in combination and in a different order than presented hereinwithout departing from the

FIG. 22 is a flowchart illustrating methods of controlling output of anelectrosurgical power generating source according to embodiments of thepresent disclosure. One approach, illustrated in FIG. 22, is todetermine one or more operating parameters associated with anelectrosurgical power generating source using image data retrieved froma medical database (e.g., image data in DICOM format stored in a PACSdatabase). This approach may be suitable, for example, in cases wherethe treatment is a second treatment (or third treatment, etc.) and wheredata associated with a prior treatment of the target tissue volume hasbeen stored in a database, or is otherwise retrievable. In accordancewith another approach illustrated in FIG. 22, one or more operatingparameters associated with an electrosurgical power generating sourcemay be determined using real-time (or near real-time) tissue temperaturedata acquired from one or more imaging modalities during the procedure,e.g., an ablation procedure.

In step 2210, an energy applicator (e.g., “E” shown in FIG. 1) ispositioned for delivery of energy to a target tissue volume (e.g., “T”shown in FIG. 1). The energy applicator may be inserted directly intotissue, inserted through a lumen, e.g., a vein, needle or catheter,placed into the body during surgery by a clinician, or positioned in thebody by other suitable methods.

In step 2220, energy from an energy source, e.g., an electrosurgicalpower generating source (e.g., 16 shown in FIG. 1), is transmittedthrough the energy applicator to the target tissue volume.

In step 2230, image data including tissue temperature information of thetarget tissue volume is acquired by imaging the target tissue volumeusing one or more imaging modalities (e.g., 30 shown in FIG. 1). Thetissue temperature information acquired by the one or more imagingmodalities may be determined by any suitable method, e.g., calculatedfrom density changes within the tissue.

In one approach, the image data including tissue temperature informationis received from one or more imaging modalities, in step 2250. Thespecific absorption rate (SAR) is calculated as a function of the tissuetemperature information from the image data, in step 2260. A possibleadvantage to taking SAR directly from the patient is that any tissueinconsistencies in the local area of the antenna or electrode would bedetected using this SAR. Calculating SAR from the electrode or antennaas it is being used in the patient may allow detection of the beginningof a non-uniform ablation field.

The SAR calculation may be performed using equation (2), where c is thespecific heat of the tissue (in units of Joules/kg-° C.), Δt is the timeinterval (in seconds), and ΔT is the temperature rise (in ° C.) withinthe time interval Δt. Equation (2) is restated below.

$\begin{matrix}{{{\Delta \; T} = {\frac{1}{c}{SAR}\; \Delta \; t}},} & (2)\end{matrix}$

which can be rewritten as follows:

${SAR} = {c{\frac{\Delta \; T}{\Delta \; t}.}}$

In embodiments, in response to early detection of a potentiallyanomalous condition, e.g., detection of the beginning of a non-uniformablation field, or under other circumstances, one or more operatingparameters associated with an electrosurgical power generating source(e.g., operably associated with the electrode or antenna) may bedetermined based on the SAR, in step 2270. Some examples of operatingparameters associated with an electrosurgical power generating sourcethat may be determined include temperature, impedance, power, current,voltage, mode of operation, and duration of application ofelectromagnetic energy.

In another approach, the image data acquired by one or more imagingmodalities, in step 2230, is stored in DICOM (Digital Imaging andCommunications in Medicine) format in a PACS (Picture Archiving andCommunication Systems) database (e.g., 58 shown in FIG. 1), in step2240. Prior to and/or during a procedure, e.g., an ablation procedure,image data associated with a prior treatment of the target tissue volumeis retrieved from the PACS database, in step 2245. As previouslydescribed above, the SAR is calculated as a function of the tissuetemperature information from the image data, in step 2260. In step 2270,one or more operating parameters associated with an electrosurgicalpower generating source may be determined based on the SAR.

FIG. 23 is a flowchart illustrating a method of controlling output of anelectrosurgical power generating source according to an embodiment ofthe present disclosure. In step 2310, an energy applicator (e.g., “E”shown in FIG. 1) including a radiating section (e.g., “R1” shown inFIG. 1) is provided. The energy applicator is operatively associatedwith an electrosurgical power generating source (e.g., 16 shown in FIG.1).

In step 2320, the radiating section of the energy applicator ispositioned at a first position for delivery of energy to a target tissuevolume (e.g., “T” shown in FIG. 1). Ultrasound or computed tomography(CT) guidance may be used to accurately guide the energy applicator intothe area of tissue to be treated. The energy applicator may beconfigured to operate with a directional radiation pattern. In someembodiments, the energy applicator is configured to operate with abroadside radiation pattern.

In step 2330, energy from the electrosurgical power generating source istransmitted through the radiating section to the target tissue volume(e.g., “T” shown in FIG. 1). In some embodiments, the electrosurgicalpower generating source is a microwave energy source, and may beconfigured to provide microwave energy at an operational frequency fromabout 300 MHz to about 10 GHz.

In step 2340, a first set of image data including tissue temperatureinformation of the target tissue volume is acquired by imaging thetarget tissue volume using one or more imaging modalities. The tissuetemperature information acquired by the one or more imaging modalitiesmay be determined by any suitable method, e.g., calculated from densitychanges within the tissue.

In step 2350, a specific absorption rate (SAR) is calculated as afunction of the tissue temperature information from the first set ofimage data. The SAR calculation may be performed using equation (2), asdiscussed hereinabove.

In step 2360, output of the electrosurgical generator is controlledbased on the calculated SAR. In embodiments, one or more operatingparameters associated with the electrosurgical power generating sourcemay be determined based on the calculated SAR. Examples of operatingparameters associated with the electrosurgical power generating sourceinclude without limitation temperature, impedance, power, current,voltage, mode of operation, and duration of application ofelectromagnetic energy.

FIG. 24 is a flowchart illustrating a sequence of method steps forperforming the step 2360 according to an embodiment of the presentdisclosure. In step 2361, the calculated SAR is evaluated according to apredetermined logical routine for determining whether a need exists tochange positioning of the radiating section. The predetermined logicalroutine may involve a variety of factors, such as, for example, heatdistribution within the tissue area that is to be destroyed and/or thesurrounding tissue, energy applicator design, number of energyapplicators used simultaneously, time and wattage, tumor size andlocation, and whether the tumor was a secondary or primary cancer.

When the evaluating, in step 2361, indicates a need to changepositioning of the radiating section, the method includes the step 2362of acquiring a second set of image data including tissue temperatureinformation of the target tissue volume by imaging the target tissuevolume using one or more imaging modalities after the radiating sectionis positioned at the second position.

The energy applicator's radiating section's position may be changed fromthe first position to a second position by rotating the energyapplicator about a longitudinal axis thereof and/or by repositioning theradiating section in tissue, e.g., a change in depth of the radiatingsection relative to a tissue surface. For example, an energy applicatorwith a directional radiation pattern may be rotated manually, orautomatically, based on the calculated specific absorption rate, e.g.,to avoid ablating sensitive structures, such as large vessels, healthyorgans or vital membrane barriers. Examples of antenna assembliesrotatable about a longitudinal axis “A-A” (shown in FIG. 25) such thatany elongated radiation lobes rotates therewith are disclosed incommonly assigned U.S. patent application Ser. No. 12/197,405 filed onAug. 25, 2008, entitled “MICROWAVE ANTENNA ASSEMBLY HAVING A DIELECTRICBODY PORTION WITH RADIAL PARTITIONS OF DIELECTRIC MATERIAL”, U.S. patentapplication Ser. No. 12/535,856 filed on Aug. 5, 2009, entitled“DIRECTIVE WINDOW ABLATION ANTENNA WITH DIELECTRIC LOADING”, and U.S.patent application Ser. No. 12/476,960 filed on Jun. 2, 2009, entitled“ELECTROSURGICAL DEVICES WITH DIRECTIONAL RADIATION PATTERN”, thedisclosures of which are incorporated herein by reference in theirentireties. Providing one or more indicia alignment marks (e.g., 810shown in FIG. 26) and/or indicia graduation marks (e.g., 880 shown inFIG. 26) to the energy applicator may aid in repositioning of theradiating section, as described later in this disclosure.

After the second set of image data including tissue temperatureinformation of the target tissue volume is acquired, in step 2362,according to an embodiment of the present disclosure, a SAR associatedwith the second set of image data is calculated as a function of thetissue temperature information obtained from the second set of imagedata, and one or more operating parameters associated with theelectrosurgical power generating source may be determined based on thecalculated SAR associated with the second set of image data. It isenvisioned and within the scope of the present disclosure that the SARmay be re-calculated, e.g., based on different image data sets acquiredover time, entirely independently of evaluation (if any) of the SAR todetermine whether a need exists to reposition the radiating section ofthe energy applicator.

When the evaluating, in step 2361, does not indicate a need to changepositioning of the radiating section, the method includes the step 2363of determining one or more operating parameters associated with theelectrosurgical power generating source based on the calculated SAR.Examples of operating parameters associated with the electrosurgicalpower generating source include without limitation temperature,impedance, power, current, voltage, mode of operation, and duration ofapplication of electromagnetic energy.

FIG. 25 shows an electrosurgical system 700 according to an embodimentof the present disclosure that includes an electrosurgical device 500with a directional radiation pattern. Electrosurgical device 500 iscoupled to a connector 16 via a transmission line 15, which may furtherconnect the electrosurgical device 500 to an electrosurgical powergenerating source 28, e.g., a microwave or RF electrosurgical generator.Electrosurgical device 500 includes an elongated body member defining abody wall surrounding a chamber, which is configured to receive at leasta portion of an energy applicator therein. The body wall is providedwith at least one opening 440 therethough to allow electromagneticenergy radiated from the energy applicator to transfer into a targetvolume of tissue. In some embodiments, the opening 440 is configured forradiating energy in a broadside radiation pattern, such as thenon-limiting example directional radiation patterns shown in FIGS. 27and 28.

During a procedure, e.g., an ablation procedure, the electrosurgicaldevice 500 of the electrosurgical system 700 is inserted into or placedadjacent to tissue “T” and energy is supplied thereto. Electrosurgicaldevice 500 may be selectively rotated about axis “A-A” (as indicated bythe bidirectional arrow) such that the directional radiation patternrotates therewith. In embodiments, the electrosurgical device 500 may beselectively rotated about axis “A-A” manually by the user orautomatically. An actuator 95 may be operably coupled to theelectrosurgical device 500 for controlling the rotation of theelectrosurgical device 500 in an automatic process. Actuator 95 may beoperably coupled to the electrosurgical power generating source 28and/or a user interface (e.g., 50 shown in FIG. 1).

FIG. 26 shows an electrosurgical device 800, which is similar to theelectrosurgical device 500 of FIG. 25, except for the indicia alignmentmark 810 and the indicia graduation marks 880 on the proximal end of theelectrosurgical device 800. Indicia alignment mark 810 and/or theindicia graduation marks 880 may be carried on or inscribed into theelongated body member of the electrosurgical device 800. In someembodiments, the electrosurgical device 800 includes a plurality ofindicia graduation marks 880 defining units of linear measure, which maybe inscribed substantially circumferentially about the elongated bodymember. Indicia graduation marks 880 may be used to indicate therelative position of the opening 440 with respect to the surface of thetissue “T”. In some embodiments, the indicia graduation marks 880 areused to indicate the position of the distal end of the opening 440relative to the surface of the tissue “T”. Indicia graduation marks 880may be arranged to form an incremental pattern using any standardmeasure of length, e.g., inches or centimeters.

In some embodiments, the electrosurgical device 800 includes an indiciaalignment mark 810, e.g., a colored stripe, which is readily visiblealong the proximal end of the elongated body member. Indicia alignmentmark 810 is positioned on the elongated body member such that thelongitudinal axis of the alignment mark 810 substantially aligns withthe longitudinal axis of the opening 440, to provide a visual cue to thesurgeon to allow orientation of the direction of flow of the energy tocoincide with the indicia alignment mark 810. As shown in FIG. 26, oneor more of the indicia graduation marks 880 may overlap the indiciaalignment mark 810. Numerical indicia (not shown) may be associated withthe indicia graduation marks 880. The shape and size of the indiciaalignment mark 810 and the indicia graduation marks 880 may be variedfrom the configurations depicted in FIG. 26.

FIGS. 27 and 28 are schematically-illustrated representations ofsimulation results showing directional radiation patterns. Theillustrated results are based on a simulation that modeled operation ofan electrosurgical device 600, which is configured to operate with adirectional radiation pattern. Electrosurgical device 600 shown in FIGS.27 and 28 is similar to the electrosurgical device 500 of FIG. 25 andfurther description thereof is omitted in the interests of brevity.

The above-described systems and methods may involve the use of dataassociated with image analysis of a thermal phantom for calculation ofSAR (e.g., used to predict a radiation pattern emitted by an energyapplicator) to facilitate planning and effective execution of aprocedure, e.g., an ablation procedure.

The above-described systems and methods may involve the use of imagedata including tissue temperature information to calculate SAR as afunction of the tissue temperature information during a procedure (e.g.,used to determine one or more operating parameters associated with anelectrosurgical power generating source). As described above, image dataincluding tissue temperature information (e.g., acquired by one or moreimaging modalities) may be stored in DICOM format in a PACS database,and the stored image data may be retrieved from the PACS database priorto and/or during a procedure, e.g., for use in calculating SAR duringthe procedure. As described above, image data including tissuetemperature information may be received from one or more imagingmodalities during a procedure, e.g., for use in calculating SAR duringthe procedure. One or more operating parameters associated with anelectrosurgical power generating source may be determined usingreal-time (or near real-time) tissue temperature data acquired from oneor more imaging modalities during the procedure, e.g., an ablationprocedure.

According to various embodiments of the present disclosure, the SARaround an energy application, as determined by the above-describedmethods, may be used to predict a radiation pattern emitted by an energyapplicator, and/or control the positioning of an electrosurgical device(e.g., rotation of a energy applicator with a directional radiationpattern to avoid ablating sensitive structures, such as large vessels,healthy organs or vital membrane barriers), and/or control anelectrosurgical power generating source operatively associated with anenergy applicator.

Although embodiments have been described in detail with reference to theaccompanying drawings for the purpose of illustration and description,it is to be understood that the inventive processes and apparatus arenot to be construed as limited thereby. It will be apparent to those ofordinary skill in the art that various modifications to the foregoingembodiments may be made without departing from the scope of thedisclosure.

1. A method of controlling output of an electrosurgical power generatingsource, comprising the steps of: receiving image data including tissuetemperature information of a target tissue volume; calculating aspecific absorption rate as a function of the tissue temperatureinformation from the image data; and determining at least one operatingparameter associated with an electrosurgical power generating sourcebased on the calculated specific absorption rate.
 2. The method ofcontrolling output of an electrosurgical power generating source inaccordance with claim 1, wherein the image data is retrieved from amedical database.
 3. The method of controlling output of anelectrosurgical power generating source in accordance with claim 2,wherein the image data is associated with a prior treatment of thetarget tissue volume.
 4. The method of controlling output of anelectrosurgical power generating source in accordance with claim 1,wherein the image data is received from at least one imaging modalityduring an ablation procedure.
 5. A method of controlling output of anelectrosurgical power generating source, comprising the steps of:positioning an energy applicator for delivery of energy to a targettissue volume; transmitting energy from an energy source through theenergy applicator to the tissue target volume; acquiring image dataincluding tissue temperature information of the target tissue volume byimaging the target tissue volume using at least one imaging modality;receiving the image data from the at least one imaging modality;calculating a specific absorption rate as a function of the tissuetemperature information from the image data; and determining at leastone operating parameter associated with an electrosurgical powergenerating source based on the calculated specific absorption rate. 6.The method of controlling output of an electrosurgical power generatingsource in accordance with claim 5, wherein the at least one operatingparameter associated with the electrosurgical power generating source isselected from the group consisting of temperature, impedance, power,current, voltage, mode of operation, and duration of application ofelectromagnetic energy.
 7. A method of controlling output of anelectrosurgical power generating source, comprising the steps of:providing an energy applicator including a radiating section, the energyapplicator operatively associated with an electrosurgical powergenerating source; positioning the radiating section of the energyapplicator at a first position for delivery of energy to a target tissuevolume; transmitting energy from the electrosurgical power generatingsource through the radiating section to the target tissue volume;acquiring a first set of image data including tissue temperatureinformation of the target tissue volume by imaging the target tissuevolume using at least one imaging modality; calculating a specificabsorption rate as a function of the tissue temperature informationobtained from the first set of image data; and controlling output of theelectrosurgical generator based on the calculated specific absorptionrate.
 8. The method of controlling output of an electrosurgical powergenerating source in accordance with claim 7, wherein the step ofcontrolling output of the electrosurgical generator based on thecalculated specific absorption rate includes evaluating the calculatedspecific absorption rate according to a predetermined logical routinefor determining whether a need exists to change positioning of theradiating section.
 9. The method of controlling output of anelectrosurgical power generating source in accordance with claim 8,wherein when the evaluating step indicates a need to change positioningof the radiating section, the method includes the step of acquiring asecond set of image data including tissue temperature information of thetarget tissue volume by imaging the target tissue volume using the atleast one imaging modality after the radiating section is positioned ata second position.
 10. The method of controlling output of anelectrosurgical power generating source in accordance with claim 9,wherein the radiating section is positioned at the second position byrotating the energy applicator about a longitudinal axis thereof. 11.The method of controlling output of an electrosurgical power generatingsource in accordance with claim 10, wherein the energy applicator isconfigured to emit a directional radiation pattern that rotatestherewith during rotation of the energy applicator about thelongitudinal axis thereof.
 12. The method of controlling output of anelectrosurgical power generating source in accordance with claim 9,further comprising the step of: calculating a specific absorption rateassociated with the second set of image data as a function of the tissuetemperature information obtained from the second set of image data. 13.The method of controlling output of an electrosurgical power generatingsource in accordance with claim 12, further comprising the step of:determining at least one operating parameter associated with theelectrosurgical power generating source based on the calculated specificabsorption rate associated with the second set of image data.
 14. Themethod of controlling output of an electrosurgical power generatingsource in accordance with claim 8, wherein when the evaluating step doesnot indicate a need to change positioning of the radiating section, themethod includes the step of determining at least one operating parameterassociated with the electrosurgical power generating source based on thecalculated specific absorption rate.